The symptoms of premenstrual syndrome consist of mood, cognitive, and behavioral disturbances occurring in the premenstrual phase of the cycle. They may become severe enough to cause suicidal depression or psychosis. Objective physiologic parameters that correlate with the subjective symptoms of PMS need to be identified in order to delineate this syndrome further and possibly to suggest better forms of treatment. First, this study will examine sleep, temperature and activity changes across the menstrual cycle in ten women with moderate to severe premenstrual syndrome and in normal volunteers. One month of baseline activity recording, objective ratings and self-ratings of sleep, mood, and energy will be obtained. Subjects will then be admitted to the hospital where they will undergo sleep EEG and temperature recordings two nights a week for the duration of one menstrual cycle. Premenstrual syndrome (PMS) may represent a variant of affective disorder. Therefore, treatment modalities found to be effective in the major affective disorders may be useful in treating patients with PMS. For example, sleep deprevation which induces transient remissions in affective disorder may do the same in PMS. Furthermore, sleep deprivation lowers prolactin, and hyperprolactinemia has been associated with mood disturbances in patients with PMS. Therefore, the effects of sleep deprivation will be investigated in these patients. Prolonged intense light exposure alleviates symptoms in patients with seasonal affective disorder. Since symptoms of SAD and PMS are similar, prolonged intense light exposure will be evaluated as a possible treatment for PMS. Results of sleep deprivation and light treatment experiment may increase our understanding of the pathophysiological mechanisms of PMS and the relationship between PMS and affective disorders.